One degree below zero was measured at O'Hare Airport Tuesday morning, ending a streak of 711 consecutive days without subzero temperatures in the city, said National Weather Service meteorologist Richard Castro. The last day below zero at O'Hare was Feb. 10, 2011, when it plummeted to 9 below.

Those who must venture out are warned to bundle up to protect themselves against frostbite, which experts say can affect exposed skin within 30 minutes in current temperatures.

Even after the alert expires, forecasters are predicting a high of just 11 degrees.

There's a chance of flurries on Wednesday, too, and a 50 percent chance of snow on Thursday night going into Friday, Castro said. It could be the city's chance to finally see snow measuring an inch at O'Hare, which hasn't happened for about 331 days.

The city provides six warming centers, in addition to facilities such as libraries and hospitals, to provide protection against the dangerous weather. The warming centers generally operate from 9 a.m. to 5 p.m., though the city's Garfield Center at 10 S. Kedzie Ave. runs 24 hours.

Chicagoans are cautioned to dress in layers, request well-being checks for those at risk, report inadequate building temperatures and avoid drinking alcohol, which can increase the risk of hypothermia.

Warming centers operated by the the Chicago Department of Family and Support Services: